A known electrophotographic image forming apparatus includes a main body and one or more photosensitive drums. Each of the one or more photosensitive drums is disposed within the main body and is configured to carry a developing agent image thereon.
For example, a color laser printer includes a drum unit and four developing cartridges. The drum unit holds four photosensitive drums. The drum unit is attachable to and detachable from a casing of the color laser printer in a sliding manner. The developing cartridges are provided for the respective photosensitive drums and are attachable to and detachable from the drum unit.
In the color laser printer, the drum unit includes side plates that support respective end portions of the photosensitive drums in a width direction of the drum unit. The developing cartridges are attached to the drum unit while being interposed between the side plates in the width direction.
Each male coupling member is coupled to a female coupling member of a corresponding one of the developing cartridges through a coupling passing hole defined in one of the side plates. The coupled male coupling member is free from forward movement and backward movement relative to the corresponding female coupling member but is not rotatable relative to the corresponding female coupling member. With this coupling, a driving force is inputted to the female coupling members from the casing of the color laser printer.